In particular, BNN [1]} directly unitize the Straight-Through-Estimator in training stage to calculate the gradient of weights and activations as
\(\begin{aligned}\frac{\partial {\bf b}^{{\bf w}_{i,j}}}{\partial {\bf w}_{i,j}} = {1}_{|{\bf w}_{i,j}|<{1}}, \frac{\partial {\bf b}^{{\bf a}_{i,j}}}{\partial {\bf a}_{i,j}} = {1}_{|{\bf a}_{i,j}|<{1}}\end{aligned}\) 
